I've been all over the place trying to shove my stuff into peoples' faces- eeer interacting with more communities o/ Here's what I've found in my travels. These are all completely subjective of course.
Fun fact, no one knows how to use G+. I certainly don't. You don't. Your brother-in-law who works for Google Plus who says he is "one of the lead developers on Google Plus"? Yeah he doesn't know how to use it either. I know he says he does. Don't trust his lies.
As far as I can tell, the big problem with G+ is, as mentioned before, the circles. You're either in the microscopic pool of your friends' serials, or you're in the huge ocean of public content. I've had links to Orbital Academy on G+ for about 9 months, and have not had a single visit from them.
I am so bad at twitter I've heard a lot of people have great success with it, but it does involve a little bit of work in a quite unique direction; you have to be pithy and interesting very consistently in small doses. I hear there are wonderful pockets of community all over the place but one needs to do the legwork to find them.
Reddit is a weird little beast. On the one hand there are a HUGE number of readers to be found here. When first starting Orbital Academy, as a complete unknown, I had spikes of 500 visitors at a time from Reddit. On the other hand, they can be extremely touchy about people who they perceive as 'taking advantage' of them (aka "you're not a real part of our community, you're just here to push your own stuff), and the backlash for that can be intense. I got really turned off of reddit after being shadowbanned (where they make your posts invisible to everyone but you, so that you don't know you're banned, but think that everyone in the community is ignoring you), because the mods of the subreddit decided that since I was posting MY sexy stories to r/sexystories, I must be focused more on my own desires rather than the community. As soon as I stopped posting regular links to OA the readership dried up almost instantly.
I think it has a lot to do with the fact that mods of subreddits have complete control over those subreddits, and if they feel that you aren't "really" part of the community they have no problem cutting you out of it, without explanation or appeal. On the other hand, I can't deny that they are excellent at providing a gigantic one-time boost of readers. I posted a link to Mage Life there once and I believe Tempest got something on the order of 3,000 views that day.
I have heard a lot of anecdotal evidence that Tumblr has great communities. Indeed, I've *seen* a lot of great communities from the outside. I just don't have enough knowledge of the medium to find those that might like me. I'll have to use your methods Dennis, see if I don't have more success there.
I'd always loved reading TVTropes, and it provides a nice steady trickle of newcomers to my serials which is nice. I think they prefer that the content creators don't add or edit their own pages though, so you're a bit at the mercy of your fans when it comes to filling it out.
Seriously this community is just awesome. A lot of my readers, when I first started out, came from links via other, more well-established serials, and I try to pay it forward when I can. If nothing else, the amount of advice, both given to me and observed, is exceedingly helpful. Thus far this is the only place beyond my comment section that feels like a "community" that I'm a part of, and I love it.
*Other serials' comments sections*
You probably wouldn't think it, but I'm actually an incredibly shy person, especially when it comes to commenting on other peoples' serials. I should probably get over this, since I know how much help it can be to have someone starting the conversation on serials where there doesn't seem to be a whole lot of it. *Maddi resolves to comment more*
*Word-of-mouth, friends, family, etc*
I wouldn't suggest relying on this to bring in readers. I've been blessed with an EXTREMELY supportive set of friends and family who regularly read my stuff, but while they are probably MY biggest fans they're nowhere near my serial's biggest fans.
All in all I think DDWebb hit the nail on the head; it can be really really hard to make the time to both write a lot AND take core of the non-writing business. I do maintain that (depending on your end goal for your serial) it *is* important to take care of that business though. The returns on your time investment are just too valuable to ignore. Thanks everyone for the advice on getting into those communities that I've been slacking in; I'll definitely be using your advice to try to nudge my way in there.